Ultrafast optical responses of image-carotene and lycopene probed by sub-20-fs time-resolved coherent spectroscopy

We investigate how structural distortions in carotenoid cause decoherences of its high-frequency vibrational modes by applying the sub-20-fs time-resolved transient grating spectroscopy to image-carotene and lycopene. The results indicate that the image central stretching mode shows significant loss of coherence under the effects of the steric hindrance between image-ionone ring and polyene backbone, whereas the other high-frequency modes do not show such dependency on the structural distortions.